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Kenwood receiver works but sounds awful -- what could be wrong?

F

fiddlerman

New Member
I own a Kenwood KR-5200 that seems to be star-crossed. Its right channel did not work when I bought it (Bay Area craigslist), so I took it a stereo repair shop in the Walnut Creek area. The technician cleaned the pots and circuit boards and restored sound to both channels. When I hooked it up at home, it was operational, but there seemed to be a high level of listener fatigue. Midrange was attenuated and there was a kind of shrill quality to the high end. It was as if a portion of the audio spectrum was depressed or missing altogether.

I called the repairman back and he was quite defensive and obstinate. Things quickly devolved into a shouting match. Suffice to say, he's not a "people person." I am never going to get satisfaction from this particular vendor. So I'm stuck with a receiver that works okay but sounds distinctly unmusical. It's my third Kenwood receiver, so I know what to expect: something warm, smooth and detailed, not shrill and chalky.

My question is this: are there objective tests you can run on a receiver that will reveal its audio flaws, ie.,dips or spikes in frequency response? What is the likely cause of the bad sound? According to the repairman, it was very rare for any '70s-built Japanese receiver to ever need new capacitors. He told me the Japanese electronics used great parts and were built to last and that re-capping a receiver was an overrated boondoggle and waste of time and money.

I'd love to bring this unit all the way back from the dead, but I've already got $150 put into it. I would possibly be inclined to go in and replace some caps myself. Maybe I just need to look for bulging/leaky caps and replace them? Where should I look first and what is the likely culprit?
 
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I asked him about that. He sort of dodged the question, then said there was no way to manually set the bias and offset. So I think the answer is no.
 
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Is this a adjustable flat-head screw or a knob? Would it be located near the power capacitors? I assume you use a multi-meter to tweak the values.
 
Just hooked up the receiver again to make sure I wasn't imagining things. Played a Horowitz/Scarlatti CD and it seems pretty well-behaved. But I just put in a Mendelssohn album with the Cleveland Orchestra. Very peaky and shrill highs, especially the violin section when turned up loud. Lack of mellow at high SPLs. It seems like the EQ for this unit has a big hump in the high end and a dip in the lower mid-range and bass. This was particularly noticable through my Polk Monitor 5s and feels a bit better with Cambridge Model Sixes, but still a problem. Would a bias adjustment mitigate this wacked out EQ and smooth out the sound? I've made some adjustments with the tone controls (treble at 10 o'clock, bass at 3), but they seem larger than I'm typically used to making.
 
Mister Fiddler,
Be aware that if you short out the pins you read the bias voltage from you can blow the outputs. The meter has to be able to read MV DC. Walmart has a TEK 10709 for $13 the last I looked. Low bias will increase distortion.
 
No, but I haven't listened to the FM very much. (There isn't much worth listening to.) I'll try that this afternoon and see. Interesting if it resided in the phono/aux inputs only.
 
I wouldn't advise someone without much knowledge to poking around inside of these things, just saying.
 
Based on questions like this:
fiddlerman said:
Is this a adjustable flat-head screw or a knob? Would it be located near the power capacitors? I assume you use a multi-meter to tweak the values.
Click to expand...

I have to agree with this :
Ken Boyd said:
I wouldn't advise someone without much knowledge to poking around inside of these things, just saying.
Click to expand...

Not to discourage anyone from trying and learning, the potential for damage to the equipment or individuals is not to be overlooked.

PROCEED WITH CAUTION !
 
Message received, guys. FYI, I am a total greenhorn. But I'm eager to learn more about restoring vintage receivers. Gotta start somewhere. At this point, all the success I've had is cleaning pots with contact cleaner. Small moral victories, but they've gotten me inside the cabinet.

To answer some of your questions: I've run two sets of speakers through this rig, a pair of Polk Monitor 5s (with Peerless tweeters) and two pairs of Cambridge Model Sixes. These are not speakers that would seem to be mis-matched with a receiver like the KR-5200. I'm pretty sure they were connected in phase, and tried switching the wire around. This did not result in any improvement.

BTW, I've run these speakers through a Harmon/Kardon 330c, a Kenwood KR-3600 and now a Kenwood KR-6160. None of the receivers listed elicited any of the negative effects displayed by the KR-5200. So I don't think it's the speakers.

I have not pushed the receiver beyond 5 out of 10 on the volume knob. Most of the unpleasant stuff came out at around 4. This is the sweet spot for most of my Kenwoods. I've found that turning the treble way down and activating the loudness seems to mitigate this strident effects, but to me this seems absurd. The receiver is clearly unsound.

My latest theory is what I've identified as an EQ problem may in fact be excessive distortion caused by some bad semi-conductors. The aural fatigue problem seems to point to this theory. What I'd like to find out from this forum is if this problem is at all uncommon. I have a practically functioning receiver that sounds crummy. It doesn't sound like my other Kenwoods, which have richly detailed and warm, pleasing characteristics. Certainly this can't be a rare issue. And if it is isn't, what then would be the usual causes?
 
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